1,5-Anhydro-2,4-dideoxy-2-(4-fluoro-5-methyl-1-oxo-6-(4-(1H-pyrazol-1-yl)benzyl)-1,3-dihydro-2H-isoindol-2-yl)-L-threo-pentitol is known to be useful as an agent for the prophylaxis and/or treatment of Alzheimer's disease and the like (Patent Document 1).